Phase 1 Study of Elotuzumab in Combination with Autologous Stem Cell Transplantation and Lenalidomide Maintenance for Multiple Myeloma

Introduction: Elotuzumab is a humanized monoclonal antibody directed against SLAMF7 that is approved for use in relapsed multiple myeloma patients in combination with lenalidomide and dexamethasone. This agent appears to have several modes of action, including facilitation of antibody-dependent, cell-mediated cytotoxicity (ADCC) through binding to SLAMF7 on myeloma cells and activation of natural killer (NK) cells to kill tumor cells through ligation of the target. We initiated a single-center, open label, phase 1 trial based on the hypothesis that the addition of elotuzumab and autologous peripheral blood mononuclear cell (PBMC) reconstitution to standard-of-care autologous hematopoietic stem cell transplantation (auto-SCT) and lenalidomide maintenance for consolidation therapy in myeloma patients after induction therapy will be safe and feasible. We hypothesize that early PBMC reconstitution post-auto-SCT will restore a viable NK cell population for activation by elotuzumab, which may target residual myeloma cells and promote tumor-specific humoral and cellular immune responses against myeloma cells. Subsequent maintenance therapy with elotuzumab and lenalidomide may amplify this response, resulting in long-term maintenance of the minimal residual disease state.

Methods. This is a Phase 1b, open-label, trial investigating elotuzumab and autologous PBMC reconstitution with auto-SCT consolidation therapy and lenalidomide maintenance. The primary objective of this study is to assess the safety and tolerability of elotuzumab and autologous PBMC reconstitution in the setting of auto-SCT and lenalidomide maintenance in multiple myeloma patients. The secondary objectives are to assess myeloma disease status and progression-free survival (PFS) after one year of treatment. Subjects must achieve partial response or better by IMWG criteria with induction chemotherapy, be eligible for auto-SCT by institutional standards, and meet inclusion/exclusion criteria. Fifteen subjects are planned in this pilot study. The treatment plan is as follows: In addition to standard peripheral blood stem cell mobilization and harvest, subjects undergo steady-state leukopheresis for PBMC collection. Subjects receive standard melphalan conditioning (day -1) and autologous stem cell rescue (day 0). Autologous PBMC are reinfused on day +3 post-stem cell infusion and cycle 1 of elotuzumab 20 mg/kg IV is given on day +4. Subjects receive subsequent cycles of elotuzumab every 28 days up to cycle 12. Lenalidomide maintenance at 10 mg orally daily days 1-21 of every 28-day cycle begins with cycle 4 of elotuzumab, and may continue off study beyond cycle 12 at the investigator's discretion. Bone marrow aspirates and peripheral blood are collected for correlative studies at screening, cycle 2, cycle 4, and at the end of study after cycle 12. For the primary endpoint analysis, the safety population includes all subjects who received at least one dose of study treatment. The evaluable population constitutes all subjects who received at least four of the first five planned doses of elotuzumab.

Results: Fourteen of the planned 15 subjects have been enrolled in the study. Demographic and staging data reflect the general transplant-eligible myeloma patient population at our institution. All 14 of these subjects are included in the safety population, having received at least 1 dose of elotuzumab. Nine of 14 subjects have completed at least 4 of the first 5 planned elotuzumab infusions and are evaluable. The majority of adverse events, including infusion reactions attributable to elotuzumab, have been grade 2 or lower. Grade 3 or higher hematologic AEs, including anemia, neutropenia, lymphopenia, thrombocytopenia, and non-hematologic AEs including nausea, vomiting, and dehydration, were attributable to the auto-SCT procedure. There were no delays in hematopoietic reconstitution observed. One episode of grade 3 hypertension was attributed to elotuzumab infusion and resolved with supportive care. No AEs were attributed to PBMC reconstitution.

Conclusions: The combination of elotuzumab and PBMC reconstitution with standard auto-SCT and lenalidomide maintenance for consolidation therapy of multiple myeloma appears to be safe and feasible. One subject withdrew for personal reasons. The trial is ongoing and is expected to complete accrual and the clinical results will be updated for presentation.